Conventionally, battery units are charged or discharged in a fixed charge/discharge pattern without caring about the deterioration of the battery units. This causes a problem that the temperature largely increases inside a battery unit resulting in a deterioration of the battery unit.
Also, in the case of battery units for automobile, it is needed to instantaneously discharge a required amount. While in many cases of stationary battery units and the like, a predetermined period of time is allowed to carry out the charge/discharge. In these cases, a charge/discharge schedule is required to carry out the charge/discharge while inhibiting the deterioration of battery units.
It is known that when battery units repeat the charge/discharge, the internal resistance thereof gradually increases while the charge/discharge capacity decreases. The increase of the internal resistance depends on the duration of time; i.e. how long a battery unit itself or battery cells themselves are placed under a high temperature condition. That is, in battery units which are placed under a high temperature condition for a long period of time, the internal resistance increases while the deterioration of the battery units is accelerated.